Explosion-proof apparatus



1945. A. A. RALSTON EXPLOSION-PROOF APPARATUS 2 Sheets-Sheet 1 FiledDec. 31, 1942 Inventor Albert A. Ralston b MW y His Attorney.

Jan. 30, 1945. A. A. RALSTON EXPLOSION-PROOF APPARATUS Filed Dec. 31,1942 2 Sheets-Sheet 2 Patented Jan. 30, 1945 EXPLOSION-PROOF Arrm'rUsAlbert A. Ralston, Fort Wayne. InlL, asslgnor to General ElectricCompany, a corporation of New York Application December 31-, 1942,Serial No. 470,815

3 Claims.

My invention relates to electrically driven apparatus, and particularlyto such apparatus which includes an electric motor and a control switchprovided with enclosures to render the apparatus explosion-proof.

It is frequently necessary to install apparatus driven by electricmotors in locations where there is a possibility of explosion due to thepresence in the air of inflammable gases or vapor in quantitiessuilicient to produce explosive mixtures. For example, it may bedesirable to provide a water cooler including an electrically drivenrefrigerating machine in a factory or other location where there isdanger of the presence of an explosive atmosphere in the vicinity of thecooler. The danger of explosion may be avoided by encasing all parts ofthe mechanism where sparks may be produced so that these sparks do notoccur in the atmosphere. However it is also desirable that the controlmechanism should be readily accessible for adjustment, repair orreplacement. Furthermore, it is desirable for convenience of manufacturethat the casing enclosing the control should be separate from the casingenclosing the motor. At the same time, the electric leads connecting thecontrol and motor must be adequately sealed to prevent propagation offlame to the surrounding atmosphere in case of an internal explosion.

It is an object of my invention to provide an improved arrangement forconnecting two casings for electric apparatus and which provides apassage for an electrical conductor between the casings.

It is a further object of my invention to provide an explosion-proofunit assembly comprising an electric motor-driven apparatus in a casing;an external control for the electric motor in a separate box; and animproved arrangement for securing the control box on the casing.

Further objects and advantages of my invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a, part of this specification.

For a better understanding of my invention, reference maybe had to theaccompanying drawings, in which Fig. 1 is a front elevation view partlyin section of a water cooler including a motor-compressor unit embodyingmy invention; Fig. 2 is an enlarged sectional view of a portion of themotor-compressor unit shown in Fig. 1; Fig. 3 is a sectional sideelevation of the unit on the line 33 of Fig. 2; Fig. 4 is an enlargedsec-- tional view on the line 4-4 or a connecting means employed in Fig.3 and shown in its initial posi tion; and Fig. 5 is a view similar toFig. 4 with the connecting means shown in its final Position.

Briefly, the motor-compressor unit illustrated in the drawings comprisesa sealed compressor and motor and an enclosed control box mounted on thesealed motor-compressor casing. The contro1 box is provided with anaccess cover or door which may be screwed tightly in place; and thecontrol box is secured rigidly on the motor-compressor casing by aplurality of motor lead sealing and connecting devices. seal thecomplementary openings in the motorcompressor casing and the controlbox, but rigid-v ly hold the control box on the unit, and also providepassage for the electrical conductors between the control apparatus andthe electric motor within the unit.

Referring now to the drawings, the water cooler illustrated in Fig. 1comprises an upright casing or cabinet Ill, in the lower portion ofwhich is provided a refrigerating machin comprising a motor-compressorunit II, and a refrigerant condenser l2. The electrical control foroperating the motor is included within a closed casing, or control boxl3, mounted on the motor-compressor unit ll. During the operation of thecooler, refrigerant is compressed within the casing of motor-compressorunit II and is discharged through a conduit (not shown) to the condenserl2, where it is liquefied and is supplied to a cooling unit orevaporator (not shown) located in the upper portion of the cabinet Ill.The evaporator absorbs heat from water circulated through a suitablewater coil or chamber in accordance with the usual practice, andvaporized refrigerant is returned to the motor-compressor unit iithrough a suction line I4. The water cooler includes a foot pedal l6connected through a rod I! to a suitable water controlling valve in theupper portion of the cabinet, and when the pedal I6 is depressed, wateris discharged from a drinking fountain bubbler 5 at the top of thecabinet. The casing of motor-compressor unit II and the control box iiiare so made and assembled as to provide a so-called explosion-proofstructure. By explosion-proof is meant that although an enclosure is notnecessarily gas-tight, it is such that if an internal explosion shouldresult from the ignition, by a spark, of an explosive gas-air mixturewithin the enclosure, the flame will be prevented from passing to thesurrounding atmosphere.

The control box ii is rigidly secured on the mo- These devices not onlyvtor-compressor II in a manner shown in Figs. 2 and 3. The casing ofmotor-compressor unit II includes an upwardly extending boss or flangeI8, the top of which is machined to provide a surface I9 for engaging acomplementary machined surface 24 of the control box I3. The control boxI3 is cylindrical in form and is provided with a cover 20 which isremovably secured on the box I3 by threads 2I. The cover 20, whenremoved, provides ready access to the interior of the control box, andwhen screwed in place provides an explosion-proof closure. Within thecontrol box is located suitable switching apparatus 22 for controllingthe motor 23 of the motor-compressor unit I I. the motor beinelectrically connected to the control through leads 25, conductor rodsor leads 26 and leads 21. The control may be made responsive to thetemperature of the cooling unit in accordance with common practice, asuitable temperature control bellows 28 being connected through apressure duct or capillary tube 29 to a control bulb or element (notshown), arranged to be responsive to the temperature of the coolingunit. The control tube 29 is secured and sealed in a metal cylinder 30by solder 3|, and the cylinder is then placed within a cylindricalopening 32 within an internal boss 33 in the casing I3. The fit betweenthe cylinder 30 and the opening 32 is sufficiently close, and the lengthof the contacting cylindrical surfaces is sufficiently great, that therecan be no propagation of flame therethrough. A power supply cable 34 forthe motor enters the control box I3 through a suitable connector 35 ofan approved explosion-proof con struction.

The connecting devices for maintaining the motor lead rods 26 inposition, and for holding the control box I3 rigidly on the motorcompressor casing II, each include an external sleeve 31 threaded in anopening 38 in the control box and an internal sleeve 39 threaded in theexternal sleeve 31 and also in an opening or passage 40 extendingthrough the flange I9 of the casing of motor-compressor unit II. Thisconstruction is clearly indicated in Figs. 4 and 5. The conductor 26passes through the inner sleeve 39 and is insulated from the sleeve andfrom the rest of the structure by a sleeve or tube 4I of rigidinsulating material which is not provided with threads. The conductor 26is also provided with a sleeve 42 of rigid insulating material at itslower end adjacent the bottom end of the opening 46 in the casing ofmotor-compressor II. The sleeves 4| and 42 do not meet within thepassage 40, but are spaced apart to provide room for a resilient sleeve43 of synthetic rubber or other suitable material. The conductor 26comprises a bolt having a head 44 at its lower end, and a threaded nut45 at its upper end. When the connection is in position, the opening 49is effectively sealed by tightening the nut 45 to compress the sleeve 43within the opening 40, and provide an effective sealing joint betweenthe lead 26 and the wall of the opening.

The lead 26 is inserted from within the motorcompressor casing II afterthe sleeves 31 and I9 have been secured in place, access to the interiorof the casing being had by removing an end closure plate 46 secured tothe casing by bolts, one of which is indicated at 41, a suitable gasket46 being provided between the cover and its seat on the casing.

During the assembly of the motor-compressor unit. the sleeve 31 isthreaded into the opening 36 until the lower end of the sleeve is flushwith the surface 24. The sleeve 39 is threaded through the sleeve 31until its lower end is flush with the end of the sleeve 31. This,of-course, may be done either before or after threading the sleeve 31into the opening 36. The sleeves of all three connectors indicated inFig. 3 are similarly adjusted and the box is then held over thesupporting.

flange I8 with the complementary openings 38 and 49 in coaxialalignment. The sleeves 31 are then rotated away from the flange I8 aslight distance, less than one thread, in order to align the threads ofthe inner sleeve 39 with the threads of the opening 40, and the sleeves39 are then threaded into the openings to their lowermost positions asindicated in Fig. 4. The relative positions of the sleeves 31 and 39 asshown in Fig. 4 then depend upon the amount of the slight rotation ofthe sleeve 31, which was necessary to align the threads of sleeve 39with those of the opening 40, it being understood, of course, that thesleeve 31 might be flush with the surface 24 if it should happen thatthe threads were in alignment at this position. The opening in thesleeve 39 and the opening 40 thus provide communication between theinterior of the motor compressor casing and the control box I3. Theexterior threads on the sleeve 31 have a pitch greater than that of theinterior threads which engage the thread on the inner sleeve 39. Afterthe control box has been secured in place with the sleeves in positionssuch as indicated in Fig. 4. the outer sleeve 31 is rotated in adirection to move it away from the flange I8. The

sleeve 39 is held stationary, and there results a differential actionwhereby the sleeve 31 tends to move out of the opening 39 at a fasterrate than it tends to move up the sleeve 39. This rotation of the sleeve31 forces the control box I3 tightly against the flange I8 and holds thecomplementary surfaces I9 and 24 rigidly in engagement; furthermore, thedifferential action of the threads results in a. tight locking of thesleeves 31 and 39 with respect to one another. The position of thesleeves after this locking action is indicated in Fig. 5.

After securing the box rigidly on the casing in the manner justdescribed, the assemblies including the conductor rods 26 and theirsleeves 4|, 42 and 43 together with an insulating washer 59 and clips 5|at the ends of the motor leads are inserted in the opening 40 and theopening in the sleeve 39. Insulating washers 52 and metal washers 53 arethen placed over the tops of the rods 26 and the nuts are then tightenedin place to compress the resilient sleeves 43 and seal the assembliesagainst a leakage of refrigerant therethrough. The assemblies thusprovide a seal against leakage of refrigerant and also electricalinsulation for the motor leads 26. After the assemblies have beensecured in place the cover 46 is secured over the end of themotor-compressor casing and the unit is ready to be connected in arefrigerating machine and charged with refrigerant.

The arrangement of the three lead assemblies. including the sleeves 31and 39, provides a seal between the motor control box and the motor andat the same time provides the connecting means for rigidly holding thecontrol box on the motor-compressor casing. No additional bolts orclamps are required. Access to the-lead and connection assemblies is hadonly through the explosion-proof cover 29, and the entire apparatus,including the control box and the motorcompressor casing, constitutes aneffective explosion proof construction. 1

From the foregoing, it is readily apparent that sembly which iseffectively sealed and which pro-1 vides ready access to its severalparts for the purpose of adjustment, replacement or repair.

While I have shown and described my invention in connection with amotor-compressor unit for water coolers, other applications will readilybe apparent to those skilled in the art. I do not, therefore, desire myinvention to be limited to the particular construction shown anddescribed, and I intend in the appended claims to cover allmodifications within the spirit and scope of m invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, first and second closed casings, electrical apparatusin said casings, said casings having registering openings providingcommunication therebetween, said casings having complementary engagingsurfaces adjacent their respective openings, and means arranged to forcesaid surfaces into engagement for securing said first casing rigidly onsaid second casing, said means including a first sleeve threaded in saidopening in said first casing and a second sleeve threaded in said firstsleeve and in said opening in said second casing, the outer threads onsaid first sleeve having a greater pitch than the threads on said secondsleeve whereby said casings may be secured together by said secondsleeve and said complementary surfaces may be forced into effectiveengagement by rotation of said first sleeve with respect to said firstcasing to move said first sleeve away from said second casing.

2. In combination, an electric motor having a closed casing and anexternal closed control box, said casing and said box having registeringopenings providing communication therebetween, said casing and said boxhaving complementary engaging surfaces adjacent their respectiveopenings, means arranged to force said surfaces into engagement forsecuring said box rigidly on said casing, said means including a firstsleeve threaded in said opening in said box and a second sleeve threadedin said first sleeve and in said opening in said casing, the threads onsaid first sleeve having a greater pitch than the threads on said secondsleeve whereby said box and said casing may be secured together by saidsecond sleeve and said complementary surfaces may be forced intoeffective engagement by rotation of said first sleeve with respect tosaid box to move said first sleeve away from said casing, an electricconductor for supplying power to said motor extending from said box tosaid motor through said second sleeve, means for sealing said conductorwithin said opening in said casing, and means for electricailyinsulating said conductor from said box and from said casing.

3. In combination, an electric motor having a closed casing and anexternal closed control box, said casing and said box having registeringopenings providing communication therebetween, a close fitting cover onsaid box for providing access to the interior thereof, said casing andsaid box having complementary engaging surfaces adjacent theirrespective openings, means arranged to force said surfaces intoengagement for securing said box rigidly on said'casing, said meansincluding a first sleeve threaded in said opening in said box and asecond sleeve threaded in said first sleeve and in said opening in saidcasing, the threads on said first sleeve having a greater pitch than thethreads on said second sleeve whereby said box and said casing may besecured together by said second sleeve and said complementary surfacesmay be forced into effective engagement by rotation of said first sleevewith respect to said box to move said first sleeve away from saidcasing, said sleeves having portions within said box accessible throughsaid cover and arranged to be engaged by a tool for rotating saidsleeves to secure them in position.

ALBERT A. RALSTON.

